Strongly adherent metallic coated article



.Fan. 8, 1952 w. H. COLBET ETAL &

k STRONGLY ADHERENT METALLIC COATED ARTICLE Original Filed June 2%, 1944;

Il I Ratented Jan. 8, 1952 UNITED sures PATENT\ OFFICE' STRONGLYAHEBENT METALLIC COATED ARTICLE William H. cameri and Arthur R. Weinrlcl.

Brackenride, and Willard L. Morgan, Enverford, Pa.,

Glass Company, Toledo,`hio, a corporation 11 Claim.

This invention relates to strongly adherent metallic coated articles and means for producing the same. It comprses a means of securing a high degree of adhesion of metallic or reflective coatings to glass, porcelain, silica mica, or other silioates or silica-containing surfaces, and has to do, more particularly. with the use of an extremely thin layer of a metallic compound such as a metallic oxide,'su1fide. sulfate or halide such as a chloride, bromide, iodide, or fluoride, as the adhesive in the application of refiective, photo- Chemical, or other types of metallic coatings on these materials.

Reflective articles such as mirrors are commonly made by the application to glass of metallic reflectve materials such as copper, silver, gold, aluminum, chromium, platinum and rhodium. Most of these materials do not actually adhere to the glass and in forming mirrors such as silver mirrors the silver is not at all stuck to the glass but is merely laid closely to the surface and held to the glass in intimate contact largely by the pressure of the atmosphere. consequently, any localized force removes the mirror layer such as aluminum, silver, copper or gold away from the surface, causing pin holes and finally "letgoes" or "blisters" throughout the mirror. In such cases the utility of the mirror is destroyed and it rapidly disintegrates. While attempts have been made in the past to protect such mirror coatings on glass from the effects of the atmosphere and more particularly from abrasion and rubbing of the mirror film ofi the glass, these attempts have generally followed the direction of applying a protective lacquer or shellac coating. such coatings, or paint coatings which are also used, however, tend to contract during the drying and formation of the protective coatng film and they further contract and expand with the humidity in the atmosphere. such contractions or expansions in the protective films are suflicient to cause localized strains or pulling effects and often the use of such lacquers or other coatings, rather than resulting in an increase in the life of the mirrors, has been found to lead to an early destruction of the mirror by pulling the mirror coatng away from the glass.

We propose to overcome the dimculties arising from lack of adhesion within glass or other mirrors and in the similar dimculties experienced with many other coatings appled to glass for other purposes. such as metallic coatings deposited upon glass supports in order to produce photoelectric surfaces or electrical resistances. We have found that various metallic compounds in z contrast to the imetals are highly adherent to glass and that extremely thin layers of these, which are also adherent to the metal coatings to be applied to glass, can be used to secure highly adherent products, exhibting the normally desired optical, electrical or other properties without any, or at least without serious, change.

We have found that the metallic oxides which are reactive with silicia. such as those of lead, silver, aluminum, magnesium, zinc, thorium, and other rare earth metal oxides, and the 'oxides of 'cadmium, antimony, bismuth, mercury, copper and other heavy metal oxides, when applied over glass or other siliceous surfaces, are extremely highly adherent to such surfaces and that furthermore they are highly adherent to the metals which may be applied to glass either by Chemical deposition, thermal evaporation, sputtering or other means. for the purposes of securing mirrors or other coated articles. In addition, we have also found that other metallic compound may be used as adhesive layers between a metal coating and a silica-containing surface, such as glass. Thus, the metallic compounds which may be looked upon as derivatives of the metallic oxides are generally highly efl'ective and we may use the suliides, sulfates, bromides, chlorides, iodides, tungstates or other compounds related to the metallic oxides which we have indicated above and derived from the indicated metals. While with ordinary metallic mirrors the coatings can readily be removed from glass by applying adhesive tape to the same and pulling this off, it is found that with our new coated articles. the adhesive tape will not pull the mirror films away from the glass because they are so tightly adhered to the same by our intermediate thin adhesive layers. Furthermore, with the new mirrors and other coated articles, a remarkably improved resistance to moisture is found so that these will withstand, in an unprotected condition, salt spray and humidity tests for considerable periods of time, whreas with the ordinary mirrors and coated articles, the water quickly works between the mirror films and the glass on 'which it lies and removes the films from the glass. In a similar way the separation difliculties experienced due to tensioned pull when protective lacquer, paint or shellac coatings are applied on the back of mirrors, have been overcome, since our reflective coatings are adhered suflicientlytightly to forces needs to be only a few molecules thick e glass may not be detectable by any optical flect; Thus, where we use extremelythin fllms og org.. ides or other compounds fon-the purpose-ofsecuras such the presence of these compounds on ing highly adherent mirrors, the mirrors pro.-

erties as to substantially completely avoid dimi sion' of reflected or transmitted light.

It is afurther object of the present inventionto provide an article in whichta reflective or metallized !lim is iirmly and substantially permanently adhered to a supporting surface preferamy-formul of siass orother siliceous duced by depositing silver or other suitable metal on the glass first covered with-a very thin metallic oxide film, are equal in reflectivity and in transmission to similar mirrors made without the very thin oxide or otherlmetallic. compound adhesive films. However, we may also use thlcker metallic oxide or metallic compound films as an ,adhesive .layer which may even be detected by the slight color' they impart to the glass and -which :may also cut down the reflectivity or transmission of light to some degree in the final produced article. Thiis. for example, with a mir'- ror', it is apparent that if our adhesive layers are .too thick, the reflectivity properties of a second surface mirror may be seriously 'or desirably cut down but at the same time it is apparent that the reflection properties of a first .surface mirror made in such a way would notparticularly be influenced by the thickness of the oxide or adhesion-securing layer. The metallic oxide or metallic sulflde or other metallic compound maybe deposited as a coating on the glass by the direct thermal evaporation under normalconditions or within a vacuum, of extremely small amounts of the desired metallic compound. This may also becarried out in accordance with the disclosure of copending application Serial No. 541965, now abandoned. In the case of oxide layers, we may produce these in position on the glass by oxidaton of extremely thin metallic layers first deposited thereon by thermal evaporation. Thus, we may first evaporate very smallamounts of aluminum, tin,- lead or -copper and then form these into the metallic oxides while on the glass surface. As examples of the compounds we may directlyevaporate onto the glasssurface by there mal `evaporation within alvacuum, we may use lead oxide,' cadmium oxidegzinc oidde, zine sulride, lead sulflde, antimony oxide, aluminum ox ide lead bromlde, magnesium fluoride, silver chloride, or lead tungstate. We may readily form coatings of lead sulfate on glass 'by first evaporating extremely small amounts of lead sulflde and thereafter oxiding this on the by exposure to the air.

glass to lead sulfate It islaxfurther object & w 4

mmisflnniy and permanently bonded to a supw i hem enti i to provide a transparent, partiall'y --or opaque film of metal in permanently adhercd relation to a surface of a support body pretor-amy formed from class or other siliceous material.

i& flk ur rc i ct of the present lnvent'ion v jmproved article in nc a m port body by an interposed or intermediate bonding layer. i v A further object of the present invention is to provide an improved article in which a'metal film is flrmly and permanen'tly bondedto a support body by an intermediate transparent bondi'ng layer. w

It is a further object otthe present inventign to provide an improved article in whicl a metal film is iirmly and permanently bondedtb a sup: port body by an interposed or intermediate trans' parent bonding layer which has no optical eitectj.

It is a feature of the present invention t pro I vide an article of the character described in lightreflective articles in which a-`fllm of metal i iscarried .by a smooth surface oi yitreous siliceous material haracterized by the'provision of a superior bond-between the vitreous siliceous body' Itis afurther object of. the' present invention to provide an article of the character described which theimproved bond between the metal film and the vitreoussiliceous ;body is obtained without sacrificingoptical properties and particularly in which the bond-is provided by an intermediate layerhetween thevitreous siliceous body and the metal film and has such physical propwhich an intermediate bonding layer is i nter posed between a smooth surface of a viti-cop; siliceous support and a metal light in which the bonding layer has a surface in 'intimate, continuous, surface to contact with the smooth surface of the vitreous siliceous bodyso as to denne therewith a smooth' continuous interface, the other surface of the ing layer being of substantially the same smoth ness as the smooth surface of the support body; and a metal light reflecting film bonded to said bonding layer, the surface of the' metalfllm adjacent the bonding layer belng in intimate, continuous, surface to surface contact therewith and denningtherewith a smootheon? tinuous interface, the other surface of said metal film being of substantially the same smoothness as the smooth surface of the support body.' 1

It is a further feature of the present invption to provide an article of the character which comprlses a vitreous siliceous support having a smooth surface, a very thin' bonding layer formed of a metallic sulflde' permanent!? bonded toth'e surface of said support, and a o: metal perman'ently bonded to the l yer. 4

The above and other objectsandfa dvantagec -of our invention will appear from the follow:-

ing description and appended claim: when considered in connection with the accomp drawingsi'orming a part 'of this speciflcatio'n wher-ein like reference characters designate co respondin p rte in the several views.

In said drawings: t

Flgure 1 is a fragmentary sectional view of a piece of glass or other siliceous material.. v Figure 2 is a view similar to Figur-el showins the glass or other siliceous material having a thin fllm or coating of a metallic compound.

Figure 3 is a fragmentary sectional view of the article of Figure 2 having a semi-transparent reflective metallic film on its surface.

Figure& is a view similar to Figura 3 showing the article having an opaque metallic surface film Figure 5 is an elevational view oi a porcelai br earthenware article, such as a vase or the like. made in accordance with our method.

Figure 6 is a 'fragmentary detail sectional view taken substantially along the line I-I of Figure 5, looking in the direction of the arrows.

Figure 'I is a vertical sectional view of a photoelectric cell made in accordance with our method and embodying the present invention.

Before explaining in detail the present invention, it is to be understood that the invention is not limited in its application to the details of construction and arrangements of parts illustrated' in the accompanying drawings. since the invention is capable of other embodiments and of being practiced or carried out in various ways. It is to be understood `also that the phraseology or terminology employed herein is for the purpose of 'description and not of limitation, and it is not intended to limit the invention herein claimed beyond the requirements of the prior art.

Referring now particularly to Figures 1, 2 and 3 of the drawings, there are illustrated certain steps of making one type or kind of article or object in accordance with the method or process of our invention, Figure 3 showing the article resulting from said method.

In Figure 1 we have shown a support article, such as a piece of glass or other siliceous material lil, to `which a surface coating is to be applied in a manner to be described hereinafter. To one face of the support n there is applied a relatively thin adhesive or bonding layer ll of a suitable metallic compound, as seen in Figure 2.

In Figure 3, a metal film i2 is shown as applied over the metallic compound layer ll, the latter being of such a nature as to cause the film i2 to firmly and substantially permanently adhere to the support article or piece ill. The film i2 may be in the nature of a semi-transparent reflective metallic film, if desired. The layer li is of such a thickness and nature as to have absolutely no optical eflect or of some greate'r thiclmess where desired.

In Figura 4, a support piece or base !3, such as glass, quartz, or other siliceous material, has applied to one face-thereof a relatively thin layer M of a suitable metallic compound over which is applied a somewhat thicker film of some suitable opaque metal. The metallic compound layer ll causes the film !5 to flrmly adhere. substantialiy permanently, to the support or base II. The layer l4 may be of such a nature and thickness as to not cause any optical eflect, or it may in other cases be thicker and bring optical eiiects with it as well as provide adhesion of the metal to the support.

In Figures 5 and 6 we have shown the application of our novel method or process to the production of a piece of earthenware or porcelain ware having a tightly or strongly adherent coating or covering. As shown, a vase or similar article, shown as a whole at IS, has a body portion s which may be formed from porcelain or earthenware, preferably glazed. to the outer surface of which is applied a relatively thin layer s of a suitable metallic compound. Laid over this layer il is a suitable metallic film or covering I! which may be partially transparent or opaque and which is caused to flrmly or strongly adhere to the surface of the vase body or support article il so that 'said fllm I! will be of substantially a permanent nature.

While wehave shown, merel by way of illustration, a vasa il. it will be understood that our method or process is equaliy applicable to the production of coated earthenware or porcelain articles or objects of various kinds, shapes and sizes.

Our improved method or process is also applicable to the production of tightly adherent coatings for various articles and devices. As an illustration, we have shown the application of the method of our invention to the production of a photoelectric cell, as well as the resultant device or article.

The photoelectric cell is shown as a whole at 20 in Figure 7. It comprises, as shown, an open top casing or housing 20a, which may be formed !rom plastic and within which is located a base piece or body 2! formed from glass or other siliceous material. Applied to the top face or surface of the glass piece 2| is a relatively thin layer 22 of a suitable metallic compound such, for example, as zinc oxide. Laid over this layer 22 and tightly adhered to the glass 2l by said layer, is a layer of silver 23 with which electrical contacts' or conductors 24 are associated. Overlying the silver layer 23 is a photoelectric layer 25 formed from some suitable material such, for example. as copper oxide.

Example 1 By way of example, we may producee an aluminum mirror by first evaporating within a high vacuum approximately 0.0033 gram of aluminum. This was deposited on glass in a vacuum of 10 to the minus 5 millimeters, the glass being 24 inches away from the tungsten fllament upon which the aluminum was heated and evaporated. This gave a coating of about .000066 gram on a square foot of glass and this coating was about 0.0003 micron thick, or a thickness of 3 angstrom units. The coating was completely invisible and upon exposure to air rapidly oxidized to aluminum oxide. The sheet of glass thus prepared was again placed within a vacuum and 2.2 grams of aluminum was then 'evaporated onto the glass from another tungsten electrode. This gave a coating of aluminum on top of the aluminum oxide which amounted to .044 gram aluminum per square foot and was 0.1750 micron thick. To all appearances, the mirror thus produced was identical with a mirror produced by directly evaporting 2.2 grams of aluminum onto glass, the refiectivity in each case being 89%. However, the mirror produced with the oxide layer next to the glass wastightly adherent and the simple aluminum mirror was relatively poor in adhesion.

Example 2 In a further example. a silver mirror was made in which 0.007 gram oi aluminum was evaporated within a vacuum from a tungsten cofl onto glass set at 12 inches from the tungsten coil and at 24 inches away. The aluminum deposit on the glass 12 inches away from the tungsten burner was .0023 micron thick while that formed on the glass 24 inches away from the tungsten burner was obviously thinner and .0006 micron thick. These aluminum deposits were then converted into aluminum oxide as more particularly set forth in copending applications Serial Nos. 541,965 and 541,966, now abandoned, by introducing oxygen into the vacuum until a pressure of 0.01 to 0.02 millimeter was developed and then an electric glow discharge of 15,000 volts was caused to pass through the vacuum chamber and to play upon the surface of the siass.

This rapidly converted the thin' aluminum films into' alu'mi'num oxide, minutes being entirely s'ifllcie'nt to do this'.` These films would appear to be about .0030 and .0008 micron thick. The vacuufn pumps were' then again started and after again securing a vacuumof to the minus 5 milliineters, there was evaporated from other t'ngsten-- calls-or fllaments approximately- 5.9 grams of silver. which gave a deposit upon the glass placed 24 inches away of 0.1- gram of silver per square foot of area, and a deposit 4 times as thick again `'onthe glass placed 12 inches from the burners or fllaments. The silver layer thus rodfcedon the glass placed `24 inches away was approxi'nately 0.'1050 micron thick. As second surface mirrors the two mirrors produced showed' a -reflectivity of 91% in the latter case and the mirror made 12 inches away from the tungste'n 'electrodesand-having a slightly thicker aluminum oxide layer on the glass showed a reflectivity of' 88%. A refiectivity of 91% is the maximum secured with a second surface silver mirror made by thermal evaporation and not r using our oxide layers on the glass. Moreover, it is to' be understood that good adhesion was secured, the deposits not beingp moved from the Example 3 'A silver' mirror wa made by first evaporating within a highrvacuum 0.011 gram of silver onto a glass placed 24 inches away from the tungsten filament. This gave a silver coating 2.2 angstrom units thick or .00022 micron thick. The silver was then converted into an invisible silver oxide film by introducing air up to a pressure 'suiilient to permit an electric glow discharge to occur within the vacuum chamber( After several minutes operation of the glow discharge the silver film was converted into silver oxide. Thereafter the chamber was again highly evacuated and from other tungsten filaments, suflicient silver was evaporated to give a silver coating on the glass of 0.1 gram per square foot. This silver mirror showed extremely high' adhesion and the coating could not b'e removedfrom the glass .by adhesive tape. The' reflectivity "of the mirror either as a first surface or 'second surface mirror was equal to that of a silver mirror, 'nainely 95% as a first surface and 91% as a second surface mirror. The coating of silver oxide thus used is only l to 2 atoms thick, being approximately 3.3 angstrom units thick. obviosly, the thickness of this film is negligible compared to thedimensions of Visible light rays which in the yellow measure 5000 angstrom units. consequently, it ,is not surprising that such a deposit as was'used in this example had no optical effect, while exerting a desirable high increase in adhesion. I

' Example 4 0.008?` gram of yellow lead oxide were evaporated from atungsten filament onto a piece of glass 24 inches away within a high vacuum chamber. The lead oxide wasevaporated directly in a high vacuum of about 10 to the minus 2 millimeters, or better, .and gave a coating on the glass` approximately 0.0002 micron thick. This coatlng could not be seen nor did it afiect the light transmissionof the glass. 8.6 grams of silver, 2.2 grams of aluminum, 7325 grams of copper, or 5.8 grams of chomium was then thermally evaporated onto this prepared glass and in each case the first and second surface -mirrors showed the normal characterlstic reflection value and properties of the ordinary'mirrors made from these metals not having the lead oxide film. In 'each case, h'cwever, the mirrors were very tightly adherent, and in 'each of these mirrors the lead 'oxide film next-to the glass was '.0002 micron thick and the metallic reflective iayer's'were 0.1750-micron thick.

. Example 5 coating. The silver mirror produced was tightly sheets.

adherent.

Example 6 Working within a high vacuum chamber with the glass piece placed 14 inches away from the tungsten heater laments, there was evaporated onto the'glass 0.004 gram of lead which was thereafter converted into lead oxide by exposure to air. The lead film, before converting to the oxide, was about .0022 micron thick and the lead oxide film should have been about .0029 micron in thickness. When this was coated with silver by thermal evaporation suflicient to give a deposit of 0.1 gram per square foot, the second surface refiectivity of the silver mirror produced was 91%. In this case no loss in reflectivity was experienced although an extreme improvement in adhesion was Secured. We may also supply the silver layer by sputtering silver onto the lead oxide coated Similar results are secured if the lead oxide coated sheets are silvered or mirrored by ordinary chemical deposition methods, as by pouring an alkaline mixture of silver nitrate and invert sugar on the precoated sheets.

Example 7 i was about .0108 micron thick did in this case decrease the reflection but its use gave a tightly adherent mirror capable of standing prolonged salt spray tests. By the use of even thicker films i of lead oxide there is not found any further improvement in adhesion but as the lead oxide films become thicker there is a greater absorption of light. Thus, evaporating 0.036 gram of lead and converting this into lead oxide, gave a, lead oxide film of 0.0260 micron thickness and there was a distinct yellowish color produced upon the glass. When this was then coated with silver to the amount of 0.1 gram per square foot, the silver mirror produced had a reflectivity of 77%. In producing the lead oxide film in this example, the lead was preferably converted into lead oxide by operating an electric glow discharge in an oxygen or air atmosphere at .02 millimeter for about 20 minutes or the lead-coated plates may be heated a short time in an oven at C. or higher.

7 'amer can' li "particularly adherentmirror suitable i'or outside use 'as store fronts `was produced by the a m-salen 'upn an opaq'ue colored Vitrolite glass, made by Libbeyr Wns-Ford Glass Company, at a distance of 14 'inches' away from a' tungsten mames: of .005 gram of tin to'give a coating of &00,292 gram per' square foot or" or .000,000314 "gram pesqu'ere centimetr; The tin was then `civerted into oxide 'either' by exposing the 'coated' plate to normal aii' or' byglowing the same with' an electric -glow discharge'ln' an air or oxyge'n'atmosphere at around ;02 millimeter pressure. On top of this tinoxide' layer which was about 5 'aigstrom units th ick there was deposited 3.5 grams of chromium to give a mirror which -had all the optical' properties' 'of an ordinary chromiim mirror of the same chromium thickn'em." The thickness of the' chromium layer in this case was 0.1060 micron." 'This was completely etched away by known 'me'thods in portions to present the chromiu'm mirror and col- 'o'red glass'in contrasting design. 4

i g Example 9- 0.010 gram of lead sulde was evporated in a high vacuum 'directly upon 'pieces of silica, mica', 'borosilicate glass, lead glass." and ordinary glass placed 24 inches away from'the tungsten "fllamen't carrying the lead sulfide' and upon the 'coated glass pieces thus Secured, there showed .no visible signs of any deposit; There was thermally evaporated immediately within the same vacuum upon this glass, an opaque deposit of aluminum; The first surface aluminum mirrors 'produced in eachecase showed a reflectivity of 89% 'and were very tightly adherent. The lead s'ulfi'd prelininary coating, amounted to .0001 gram per 'square foot of 'area and was about .0003 'micro'nthich i Example 10 An ordinary piece of glass' was coated as under the lasfexample, but the amo'unt of lead sulfide evaporated was .025 gram. -After the evaporalion, an: was let into the tani: and after a few inoments the vacuum pumps were again started 'anda'luminum was then thermally deposited as before. This gave a similar mirror tothe last prepared glass mirror in which the al'uminum was adhered to the glass by a thin film of lead sulfate formed by oxidation of the lead sulfide. The lead sulfate layer would appear to have been of about .0011 micron thickness. The oxidation of the lead sulfide layer to lead sulfate may also be accompished without removing the piece from the vacuum chamber, by introducing air or oxygen into the chamber after the lead sulfide has been deposited, until a suflicient pressure has been built up which will permit an electric glow discharge to pass through the gases within the chamber. After a short time the electric glow dlscharge, in combination with the oxygen present, converts the lead sulflde to lead sulfate.

Example 11 "application of 5,000 to 30,000 volts of electricity at approximately one to 5 kva.

After a few minutes operation of the glow discharge, the extremely thin deposit of zinc was converted into a zine oxide layer 22 of about .0004 micron coated glass.

thickness. A silver electrode was then. energized by a high potential electric current so as to cause silver to be sputtered on top of the zinc oxide After a suflicient amount of silver 23 had been deposited the mirror coated glass or the `like 2| was found to be directly applicable for use as an electric resistance by attaching suitable conducting leads 24 to this silver film 23, as seen in Figure 7 of the drawings. Pieces of this glass were also further coated by thermal evaporation preferably within a higher vacuum with a further layer of copper oxide 25 to p'roduce a photoelectric cell, shown as a whole at 20. when suitably mounted within a case 2l|a and when the conducting silver hacking of the copper oxide was attached to suitable electrically conducting leads 24.

Both of the articles produced as just described in Example 11 were found to be highly serviceable due to the high degree of adhesion Secured, whereas in the past, it has not been possible to make such articles from silver although its high electrical conductivity made this desirable because the silver films in practical commercial use soon separated from the glass because of lack of adhesion.

Example 12 A thin film of magnesium fluoride 0.0009 micron thick was deposited upon a support of glass by thermal evaporation and thereafter a layer of silver of 0.0900 micron thickness was similarly deposited by thermal evaporation. This gave a 'strongly adherent silver mirror which could not be pulled off the glass by adhesive tape. While the thinmagnesium fiuoride film gave a high degree of adhesion to the mirror it did not interfere with or alter the reflectlve properties of the silver mirror as contrasted with similar mirrors made without such film.

Example 13 A film of silver chloride 0.0025 micron thick was evaporated upon pieces of glass within a. high vacuum. These glass pieces were then placed upon a chemical silvering table and silvered by pouring thereon a suitable freshly made mixture of caustic soda,- silver nitrate and invert sugar which precipitated thereon an opaque reflective deposit of silver in accordance with the well known means of producng silver mirrors. The second surface silver mirror produced had a reflectivity of approximately 92% and in contrast to the ordinary chemical silver mirrors the silver film could not be stripped away from the glass by adhesive tape. This silver mirror also showed remarlrably improved reslstance to salt spray as compared with ordinary chemical silver mirrors. In a similar way other chemical silver or other chemically deposited mirrors may be made which are of high adhesion using a precoated glass carrying one of our desired metallic compounds. It is necessary, of course, to choose as the metallic compound to be used on the glass one which is not soluble in the chemical solutions used for producing the mirrors. Thus, we have used silver chloride in the above example as it is not soluble in the solutions used. Thus, we may also have used in this way glasses which were precoated with silver oxide.

mesues:

Example 14 A porcelain vase as shown in Figures and 6 of the drawings was placed within a small furnace in the bottom portion of which a container carrying lead chloride was placed. The temperature of the fumace was gradually raised to bring the same to 1000 C. or 'slightly above. At these temperatures the lead chloride volatilizes and after the furnace was again cooled a thin coating of lead chloride condensed all over the surfaces of *the bowl. The bowl was then placed in a high vacuum chamber and an opaque deposit of gold was then evaporated onto the surfaces of the bowl by thermal evaporation. The gold coating was then found to be highly adherent to the porcelain bowl whereas similar bowls coated directly with gold did not give a commercial article in that the gold soon became detached and even tended to rub oil'. The thin lead chloride film acts as a strong adhesive cementing the metallic gold to the siliceous porcelain surface of the bowl. Many similar articles can be produced in such ways.

Example Plates of glass were placed within a furnace and raised to a temperature exceeding 500 C. A small amount of arsenic oxide was then blown into the furnace and at these temperatures it completely evaporates. On cooling the furnace down the arsenic oxide deposited a thin film on the glass. We have found such glass prepared with arsenic oxide or other metallic compound layer to be extremely satisfactory for applying metallic deposits thereto by the hot spray gun type ofprocess. Thus, with a suitable spray gun we may introduce copper wire through a flame and melt and atomize the copper and project it as a molten spray upon the glass which we have previously coated with arsenic oxide or other desired metallic compound material. The glass thus coated with copper may be applied for a number of uses, as for example, in burglar-proof alarms where the copper areas upon the glass carry a suitable electric current which is interrupted when the glass window or other area becomes broken; The

copper or other metals thus applied are extreme- Example 16 Clean glass pieces were coated with a layer of lead oxide 0.0002 micron thick as under Example 4 and other pieces were coated in another chamber with lead sulilde 0.0003 micron thick as in Example 9 by the direct thermal evaporation of these materials. In each case after these metallic compounds had been deposited on the glass by thermal evaporation there was then evaporated thereon within the respective chambers without breaking the vacuums, a refiective coating of rhodium. In contrast to similar deposits of rhodium made directly onto glass which are very poor in adhesion and undependable, our mirrors were of high adhesion and high service life. The intermediat coatings were transparent. invisible and without optical efiect. the first and second surface refiectivities equalling good rhodium closure herein exhibit very great resistance to 73 separation -of the metal film from the support body. and thisisaccomplished without, in any way detracting from optical properties. exhibited by similar articles previously producedwithout the inclusion of the improved bonding layer.. In the foregoing' speciflcation .mentionhas. been made of the fact that the bonding layer is da'- posited upon a smooth surface of a support body. In this connection it may be statedthat the'term "smooth surface" is used in its'ordinary sense` and need be only sumciently 'smooth to prevent visible or optically apparent light diflusionat the surface. However, the .present invention con:- templates that the specific smoothness ofjlthe surface of the support body will bereproduced'in the outer surface of the bonding layerand will also result in interfaces at opposite sides-otth bonding layer between the bonding layer and 'the support body and between the bonding layer .and the metal film of substantially the same smooth ness as the smoothness of the smooth surface 'of the support body. Thus if the" smooth surface` of the support body is polished to havean ex.- tremely smooth finish, this finish will be repi-o duced in the interfaces between the bonding layer and' the support body. between the bonding layer and the metal reflecting film, and .also at..:the outer surface of the metal reflectingfillm; Aecordingly,. the present invention results in. an article which reflects light or .which partially re flects and partially transmits light in a' manner to show no additional visible diflusion dueto the provision of the intermediate bonding layer.-,. ;i the critical surface or surfaces of the support body are highly polished. both of theinterfaces at opposite sides of the bonding layer willexhibit substantially the same property of smoothness and in addition the outer surfaces ofl the metal film will exhibit substantially the sameproperty of smoothness.

Since the adhesive layer is deposited on a smooth surface of the support body, and the metal film is deposited on the smooth 'surface of the adhesive layer without' the possibility' of intermingling or mechanically interlocking" in either case, and since the possibility'-'of chemica'l reaction between the solid adhesive layer and the solid vitreous siliceous material and the' solid metal of the film is eliminated; it is apparent that the extremely effective adhesion obtained'is primarily the result of inherent moleularforces of attraction between the materials-'j i So that there 'can be no misunderstanding 'as to the use herein of the term "siliceous material; we submit below a deflnition 'of this 'term:

The adhesive effects are secured upon -silica, silicates such as mica which contains silica,`alu minumsilicate or calcium silicate 'surfaces; and

'upon the various types'of glass which""conta in diflerent amounts of silica. Thus, 'with thele'ad glasses which have 30 to per cent silica.' 'with the optical glasses of 50 per cent silica or'more, the ordinary lime glasses of around `to '15` per cent sflica, and with the borosilicateglasses ofas high as per cent silica. we secure equally as good results as are found with pure silica. Like- -wise, the 'commercial porcelainand earthenware articles which' contain varying amountsofsilica in the ware or in the glazes provide sultable' support bases to which metallic films may -be adhered .by use of our metallic compounds. r ;2:

' This application is a division of prior copendin application Serial No. 541.964 filed-'June :24,11944, now Patent No. &482.054 dated *September-.13.13.

&BOLMB what we claim as our invention is: 1. A bonded mirror comprising a vitreous siliceous support body having a smooth cont nuous surface; a continuous intermediate, transparent,

invisible, colorless metal sulflde adhesive layer having a thickness of the order of a few molecules permanently and directly adhered by molecular forces to the smooth continuous surface of said support body without intermingling into the material of the support body, the adjacent surfaces of said support body and said adhesive layer being in intimate continuous surface to surface contact and deflning a smooth continuous interface, the other surface of said adhesive layer being of substantially the same smoothness as the said smooth surface of the support body; and a metal reflecting film permanently and directly adhered by molecular forces to said adhesive layer, the adjacent surfaces of said adhesive layer and said reflecting film being in intimate continuous surface to surface contact and defining a smooth continuous interface, the other surface of said reflecting film being of substantially the same smoothness as the said smooth surface of the support body, said adhesive layer being of a thickness invisible to the naked eye and without optical or color effects upon the transmission and reflection eharacteristies of the mirror when the mirror is viewed from a side upon which light is incident.

2. A bonded mirror comprising a vitreous siliceous support body having a smooth continuous surface; a continuous intermediate, transparent, invisible, colorless adhesive layer having the thickness of the order of a few molecules rormed of a metal sulfide selected from the group con- I sisting of lead, zine and antlmony sulflde permanently and directly adhered by molecular forces to the smooth continuous surface of said support body without intermingling into the mate rial of the support body, the adjacent surfaces of said support body and said adhesive layer being in intimate continuous surface to surface contact and defining a smooth continuous interface, `the other surface of said adhesive layer being of substantially the same smoothness as the said smooth surface of the support body; and a metal refiecting film permanently and directly adhered by molecular forces to said adhesive layer, the adjaeent surfaces of said adhesive layer and said refleeting film being in intimate continuous surface to surface contact and defining a smooth continuous interface, the other surface of said refleeting film being of substantiall the same smoothness as the said smooth surface of the support body, said adhesive layer being of a thickness invisible to the naked eye and without optical or color effects upon the transmission and reflection eharacteristies of the mirror when the mirror is viewed from a side upon which light is incident.

3. A bonded mirror comprising a vitreous silic-eous support body having a smooth continuous surface; a continuous intermediate, transparent, invisible, colorless lead sulfide adhesive layer having a thickness of the order of a few molecules permanently and directly adhered by molecular forces to the smooth continuous surface of said support body without intermingling into the material of the support body, theadjacent surfaces of said support body and said adhesive layer being in intimate continuous surface to surface contact and deflning a smooth continuous interface, the other surface of said adhesive layer beins of substantially the same smoothness as the said smooth surface of the support body; and a metal reflecting film permanently and directly adhered by molecular forces to said adhesive layer, the adjaeent surfaces of said adhesive layer and saidrefieeting film being in intimate coni tinuous surface to surface contact and deilnine a smooth continuous interface, the other surface of said reflecting film being of substantially the same smoothness as, the said smooth surface of the support body, said adhesive layer being of a thickness invisible to the naked eye and without optical or color effects upon the transmission and' reflection eharacteristies of the mirror when the .mirror is viewed from a side upon which light is incident.

4. A bonded mirror comprising a vitreous siliceous support body having a smooth continuous surface; a continuous intermediate, transparent, invisible, colorless lead sulflde adhesive layer having a thickness of the order of a few molecules permanently and directly adhered by molecular forces to the smooth continuous surface of said support body without intermingling into the material of the support body, the adjacent surfaces of said support body and said adhesive layer being in intimate continuous surface to surface contact and deflning a smooth continuous 'interface, the other surface of said adhesive layer being of substantially the same smoothness as the said smooth surface of ,the support body; and an al-uminum reflecting film permanently and direct ly adhered by molecular forces to said adhesive layer, the atu acent surfaces of said adhesive layer and said reflecting film being in intimate eontin uous surface to surface contact and deflning a smooth continuous interface, the other surface of said reflecting film being of substantially the same smoothness as the said smooth surface of the support body. said adhesive layer being of a thickness invisible to the naked eye and without optical or color effects upon the transmission and reflection eharacteristies of the mirror when the mirror is viewed from a side upon which light is incident.

5. A bonded mirror eomprising a vitreous siliceous support body having a smooth continuous surface; a continuous intermediate, transparent, invisible, colorless zine sulflde adhesive layer having a thickness of the order of a few moleeules permanently and directly adhered by molecular forces to the smooth continuous surface of said support body without intermingling into the material of the support body, the adjacent sur faces of said support body and said adhesive layer being in intimate continuous surface to surface contact and deflning a smooth continuous interface, the other surface of said adhesive layer being of substantially the same smoothness as the said smooth surface of the support body; and a metal reflecting film permanently and directly adhered by molecular forces 'to said adhesive layer, the adjacent surfaces of said adhesive layer and said refiecting film being in intimate continuous surface to surface contact and deflning a smooth continuous interface, the other surface of said reflecting film being of substantially the same smoothness as the said smooth surface of the support body, said adhesive layer being of a thickness invisible to the naked eye and 6. A bonded mirror compriing a vitreous siliceous support body having a ,smooth continuous surface; a continuous intermediate, transparent. invisible, colorless antimony sulflde adhesive layer having a thickness of the order ofa few molecules permanently and directly adhered by molecular forces to the smoothcontinuoussurface of said support body without intermingling into the material of the support body.- the adjacent surfaces of said support body and said adhesive layer being in intimate continuous surface to surface contact and defining a smooth continuous interface, the other surface of said adhesive layer being of substantially the same smoothness as the said smooth surface -of the support body; and a metal refleoting film permanently and directly adhered by molecular 'forces to said adhesive layer, the adjacent surfaces of said adhesive layer and said refiectingfilm being in intimate continuous surface to surface contact and defining a smooth continuous interface, the other surface of said refiecting film being of substantially the same smoothness as .the said smooth surface of the support body, said adhesive layer being, of athickness invisible to the naked eye and without optical or color effects upon the transmission and reflectioncharaeteristics of the mirror when the mirror is viewed from a side upon which light is incident.

7. A bonded second surface mirror comprising a transparent vitreous siliceous support body having a smooth continuous rear surface; a substantially transparent, invisible, colorless continuous intermediate metal sulilde adhesive layer having a thickness of the order of' a few molecules permanently and directly adhered by molecular forces to the rear surface of said support body without intermingling into the material of the support body, the adjacent surfaces of said support body and said adhesive layer being in intimate continuous surface to surface contact and defining a smooth continuous interface, the other surface of said adhesive layer being of substantially the-same smoothness-as the said rear surface of the support body; and a metal reflecting film permanently and directly adhered by molecular forces to said adhesive layer, the adjacent surfaces of said adhesive layer and said refiecting film being in intimate continuous surface to surface contact and defining a smooth continuous interface', said adhesivelayer being of a thickness invisible to the naked eye and without optical or color effects upon the transmission and reflection characteristics of the mirror when viewed through the front surface of saidbody.

8. A bonded article -comprising a transparent vitreous siliceous support body having a smooth continuous surface; a subs'tantially transparent, invisible, colorless'continuousintermediate metal sulfide adhesive layer having a thickness of the order of a' few molecules permanently and'directly'adhe'red by molecular forces to the smooth continuous surface of said support body without intermingling' into the material of the support body, the adjacent surfaces of said support body and said adhesive layer being in intimate contimous surface to surface'contact and defining a directly" adhered by molecular forces tosaid adhesive layer, the adjacent surfaces of' 'said' adhesive layer 'and said film being in intimate'com" tinuous surface to surface contact and defining a smooth continuous interface, the other surface of said film being of substantially the same smoothness as the said smooth surface of the support body, said adhesive layer being oi' a thickness invisible to the naked eye and without opticai or color effects upon the transmission and reflection characteristics of the mirror when the mirror is viewed from a side upon which light is incident.

9. A bonded second surface mirror comprising a transparent vitreous siliceous support body having a smooth continuous rear surface; a continuous, intermediate. transparent, invisible colorless metal sulflde adhesive layer having a thickness of the order of a few molecules permanently and directly adhered by molecular forces to the rear surface of said support body without intermingling into the material of the support body, the adjacent surfaces of said support body and said adhesive layer being in intimate continuou surface to surface contact and defining a smooth continuous interface, the other surface of said adhesive layer being of substantially the same smoothness as the said rear surface of the support body; and a metal refiecting film permanently and directly adhered by molecular forces to said adhesive layer, the adjacent surfaces of said adhesive layer and said reflecting film being in intimate continuous surface to surface contact and defining a smooth continuous interface, said adhesive layer being of a thickness invisible to the naked eye and without optical or color eifect upon-the transmission and 'reflection characteristics of the mirror, when viewed through the front surface of said support body.

10. A bonded article comprising a vitreous siliceous'support body having a smooth continuous surface; a continuous intermediate, transparent, invisible, colorless metal sulflde adhesive layer having a thickness of the order of a few molecules permanently and directl adhered by molecular forces to the smooth continuous surface of said support body without intermingling into the material of the support body, the adjacent surfaces of said support body and said adhesive layer being in intimate continuous interface, the other surface of said adhesive layer being of substantially the same smoothness as the said smooth surface of the support body; and a metal film permanently and directly adhered by molecular forces to said adhesive layer, the adjacent surfaces of said adhesive layer and said film being in intimate continuous surface to surface contact and deflning asmooth continuous interface, the other surface of said filmbeing of substantially thesame smoothness' as the said smooth surface of' the 'support body, said adhesive layer being of a thiclm'ess-invi'sibie to' the naked eye and without optical or' color effects upon the transmission and reflection characteristics of the mirror when the mirror is viewed from a side upon which light is incident' v 4 11, A bonded article comprising'a vitreoussiliceous support' body having a smooth continuous surface; a 'continuous' intermediate, transparent, invisible, colorless metal 'sulfid'e adhesive layer having a thickness-of the order of a few molecules 'permanently and directly adhered' to 'the smooth continuous surface of said support body withoutdntermingling into the material of the support body, the adjacent surfaces of said support' body ai'd'said adhesive layer being in intimate 'continuous surface to surface' contact and 17 deflning a smooth continuous interface. the other surface of said adhesive layer being of substantially the same smoothness as the 'said smooth surface of the support body; and a metal reflecting film permanently and directly adhered to said metal sulflde adhesive layer, the adjacent surfaces of said adhesve layer and said reflectin film being in intmate continuous surface to surface contact and defining a smooth continuous interface, the other surface of s'aid reflecting film being of substantiallythe same `smoothness as the said smooth surface of the support body, the intermediate metal suiflde layer constituting the sole material between the support and metal film and adhering said support and metal film together, said adhesive layer being of a thickness invisible to the naked eye and without optical or color effects upon the transmission and reflection 18 characteristic of the mirror when the mirror is viewed from a side upon which light incident.

WILLIAM H. COLBERT. ARTHUR R. WEINRICH. WILLARD L. MORGAN.

REFERENCES CITED The following references are of record in file of this patent:

UNITED STATES PATENTS the 

1. A BONDED MIRROR COMPRISING A VITREOUS SILLICEOUS SUPPORT BODY HAVING A SMOOTH CONTINUOUS SURFACE; A CONTINUOUS INTERMEDIATE, TRANSPARENT, INVISIBLE, COLORLESS METAL SULFIDE ADHESIVE LAYER HAVING A THICKNESS OF THE ORDER OF A FEW MOLECULES PERMANENTLY AND DIRECTLY ADHERED BY MOLECULAR FORCES TO THE SMOOTH CONTINUOUS SURFACE OF SAID SUPPORT BODY WITHOUT INTERMINGLING INTO THE MATERIAL OF THE SUPPORT BODY, THE ADJACENT SURFACES OF SAID SUPPORT BODY AND SAID ADHESIVE LAYER BEING IN INTIMATE CONTINUOUS SURFACE TO SURFACE CONTACT AND DEFINING A SMOOTH CONTINUOUS INTERFACE, THE OTHER SURFACE OF SAID ADHESIVE LAYER BEING OF SUBSTANTIALLY THE SAME SMOOTHNESS AS THE SAID SMOOTH SURFACE OF THE SUPPORT BODY; AND A METAL REFLECTING FILM PERMANENTLY AND DIRECTLY ADHERED BY MOLECULAR FORCES TO SAID ADHESIVE LAYER, THE ADJACENT SURFACES OF SAID ADHESIVER LAYER AND SAID REFLECTING FILM BEING IN INTIMATE CONTINUOUS SURFACE TO SURFACE CONTACT AND DEFINING A SMOOTH CONTINUOUS INTERFACE, THE OTHER SURFACE OF SAID REFLECTING FILM BEING OF SUBSTANTIALLY THE SAME SMOOTHNESS AS THE SAID SMOOTH SURFACE OF THE SUPPORT BODY, SAID ADHESIVE LAYER BEING OF A THICKNESS INVISIBLE TO THE NAKED EYE AND WITHOUT OPTICAL OR COLOR EFFECTS UPON THE TRANSMISSION AND REFLECTION CHARACTERISTICS OF THE MIRROR WHEN THE MIRROR IS VIEWED FROM A SIDE UPON WHICH LIGHT IS INCIDENT. 